In general, recent increase of illegitimate copying and purchase of digital contents through the use of Internet has intensified a demand for a technology capable of protecting intellectual property.
Unlike off-line contents, digital contents on the web can be easily copied and distributed all through the Internet. Thus, various technologies have been developed in order to protect intellectual property in the Internet environment. Among such technologies, there exist an encryption system, an access control system and a copyright marking system.
The encryption system and the access control system, however, are rarely utilized in recent years since they have a defect that contents can be illegally copied after being legally decoded.
On the other hand, the copyright marking system is gaining popularity since it employs a technique for directly embedding information to a media itself and, thus, can provide legal evidence in case a litigation for a literary piracy occurs, thereby contributing to finding out a copyright holder and an illegitimate distributor of contents.
More specifically, the copyright marking technology can be classified into a watermarking technique, a fingerprinting technique, etc.
The watermarking technique is used to prove only the property of contents by embedding information of an owner of the property to contents. Since, however, the same information, i.e., the owner information, is uniformly embedded to digital contents to be sold, all of the watermark embedded digital contents are undistinguishable from each other. For the reason, the watermarking technique is considered as a passive way to protect the property.
The fingerprinting technique, on the other hand, serves to find out a re-distributor of illegally copied contents by embedding information of a legitimate purchaser to the contents. Fingerprinted contents can be distinguished from each other since it is purchaser information, not property owner information, which is embedded to the digital contents. Therefore, the fingerprinting technique is a more active way of protecting intellectual property than the watermarking technique.
The fingerprinting technique involves three steps of generating, embedding and extracting user information by using an encryption protocol. The user information is embedded to contents by using a user key of a purchaser of the contents and the user key information is preserved in order to use later to trace a distributor of illegal copies of the contents.
Further, there is prepared a registration center (RC) between a seller and a purchaser, which takes charge of generating and embedding a user key, i.e., seller information, thereby allowing to obtain evidence of an illegal purchaser of illegally copied contents, if any.
However, the conventional technologies using the encryption protocol as described above have a defect in that digital contents can be illegally copied after being legally decoded and, further, a new user key can be generated by colluding user keys which have been respectively allotted to individual purchasers. Furthermore, since the fingerprinting technique using the encryption protocol is time-consuming in performing an embedding process due to its use of the encryption protocol, a quality of service (QOS) may be deteriorated in view of the fact that an e-purchase on the Internet should be processed on a real time basis.
In Eurocrypt97 (1997), there is disclosed a technology for preventing illegitimate distribution of contents by using such a conventional fingerprinting system, entitled “Anonymous Fingerprinting”.
The anonymous fingerprinting is a fingerprinting technique using an encryption protocol. Purchaser information is attached to purchased contents. Thus, if the contents are illegally copied and distributed, a legitimate purchaser can be distinguished from illegitimate purchasers by extracting the purchaser information that has been embedded to the contents earlier.
To be more specific, a purchaser of certain contents registers his own purchaser information at a certified registration center. Then, the registered purchaser information is fingerprinted to the contents. A seller generates purchase information including the purchaser information registered at the registration center and, then, embeds to the sold contents the generated purchase information. Then, the seller distributes the purchase information embedded contents after encrypting the contents by using a user's key. If a redistributed content is founded, the seller extracts the embedded information from the redistributed content and sends the extracted information to the registration center to identify the legitimate purchaser of the contents.
In other words, the purchaser information serves as a single fingerprinting data to identify the purchaser. The purchaser information is embedded to contents when the contents are purchased. This system, however, does not specify where to embed the purchaser information but just suggests a simple transaction method between a seller and a purchaser, which uses an encryption technique.
Further, since multimedia data such as image and audio data is redistributed in a decoded state unlike general software, it is impossible to maintain the purchaser information as fingerprinting information. Therefore, another type of fingerprinting embedding and extraction technique is required in order to use the purchaser information as a fingerprinting data for the multimedia data such as image and audio data.
As described above, the prior-art technologies for protecting intellectual property exhibit drawbacks in that digital contents can be illegally copied after being legally decoded by making use of an encryption technique and, further, a new user key can be generated by colluding user keys already allotted to purchasers.